1. Field of the Invention
The present invention relates to a signal processing apparatus, a droplet ejection apparatus, and a signal processing method.
2. Description of the Related Art
There has been known a droplet ejection apparatus in which by applying a voltage to a piezoelectric element to deform the piezoelectric element, a droplet is ejected (e.g., see Japanese Patent Application Laid-Open (JP-A) No. 2000-94670).
FIG. 12 is a circuit diagram showing a configuration example of a conventional drive circuit that applies a voltage to a piezoelectric element in a droplet ejection apparatus.
As shown in FIG. 12, this drive circuit 300 includes a digital/analog converter 302, an operational amplifier 304, and a current amplifier circuit 306. The digital/analog converter 302, an operational amplifier 304 and the current amplifier circuit 306 are connected in series. Moreover, piezoelectric elements 310 are each connected to the current amplifier circuit 306 via a switching element 308.
When a digital signal indicating a voltage as a reference of a voltage to be applied to each of the piezoelectric elements 310 is input to the digital/analog converter 320, the digital signal is converted to an analog signal in the digital/analog converter 302. The voltage of the analog signal is amplified by the operational amplifier 304 and the current thereof is current-amplified by the current amplifier circuit 306 to be output to each of the switching elements 308.
Each of the switching elements 308 switches between two states of a conduction state and a disconnection state according to a control signal (not shown), and when the switching element 308 is in the conduction state, the voltage of the analog signal output from the current amplifier circuit 306 is applied to the piezoelectric element 310.
The drive circuit as described above is generally configured on one circuit board, and thus even if some of components which configure the drive circuit have trouble, the whole drive circuit is exchanged. In this case, components which do not have any trouble are also consequently exchanged, which incurs waste in cost.
As a method for avoiding such a situation, a method in which the drive circuit is divided to make plural circuit boards and only the circuit board including the component having trouble is exchanged is considered. In this case, as a position where the drive circuit is divided, a position between the operational amplifier and the current amplifier circuit, and a position between the digital/analog converter and the operational amplifier are considered. In the former portion, a connection line for passing current to NPN and PNP transistors needs to be thicker and shorter, and a negative feedback loop also needs to be shorter for avoiding noise contamination than in the latter position. In view of these, the latter position is preferable.
In the case where the respective circuit boards obtained by dividing the circuit board on which the above-described drive circuit is configured between the digital/analog converter and the operational amplifier are connected via a connector, if a connection condition between the circuit boards is favorable, the voltage for drive is applied to the piezoelectric element via the switching element by putting a drain-source area of the switching element into a conduction state. In a conventional drive circuit, control is performed so as not to generate a potential difference in the drain and source area of the switching element.